Coupling pins which are designed to couple two or more elements and bear shear loads caused by the coupling thereof, comprise a body portion (typically, though not restricted to, cylindrical) and often means for securing the pin at its assembled position, to thereby prevent its unintentional displacement. Such means can be, for example, retention pins (cotter keys) extending through the pin's body adjacent receptive ends thereof, snap rings, screw coupled nuts, etc.
Pins, of a type which is to be discussed in this specification, may comprise a body portion having a substantially polygonal or cylindrical shape. The cross-section of the body portion is dimensioned to fit to the aperture within which the pin is intended to be inserted. For example such cross-section may be circular, in which case the regular-shaped body will be cylindrical. Thus this specification is concerned with, inter alia, pins having a polygonal or cylindrical body portion, having a nominal diameter, a base portion, having a first diameter greater then said nominal diameter, and a tapered head, ending in a second diameter smaller than the nominal diameter.
It is appreciated that pins of having a design similar to that described above but having an appropriate size may be used to fasten both small items, such as the components of an office stapler, or much larger items, such as building construction machinery, if the pin's material type and construction are adapted to withstand the expected respective forces to which the pin will be subjected.
An example of building construction machinery that uses pins to fasten objects together is a tower crane. In order to withstand large shear stresses, such as those caused by heavy machinery, pins used therefor are generally made of single solid steel element free of voids which may reduce the pins shear stress/load bearing capacity. However, it should be noted that the material from which pins are made is a routine design choice, dependent on cost and the load bearing requirements of the pin.
U.S. Pat. No. 5,000,610 discloses a stop pin which has a forward end and a latching end is employed between spaced plates or walls having aligned apertures. The latching end of the stop pin has locking buttons formed on longitudinal faces of the stop pin and a shoulder spaced from the locking buttons by the thickness of the first plate. The forward end of the stop pin is inserted through the first aperture and into the second aperture. Additional axial force on the stop pin forces the lock button through the first aperture by rotating the latching end into relieved portions of the first aperture while the forward end of the stop pin opposes rotation. After the stop buttons pass through the first plate the pin straightens and is latched with the stop button and the shoulder on opposite sides of the first plates/U.S. Pat. No. 3,511,388 discloses another type of locking mechanism in which a pin has cotter keys inserted into both the base portion and the tapered head portion thereof. The inserted cotter keys serve to increase the diameter of the portion of the pin to which they are attached thereby halting the pin's motion into the aperture within which it is inserted.
GB Patent Serial No. 1,093,679 discloses (see FIG. 1) a tower crane comprised of, inter alia, mast sections 1 (which when assembled form a mast or tower), a base, a jib (working arm—a horizontal section at the top of the tower that is used to hoist the load), a machinery arm (a weight bearing horizontal section used to counterbalance the jib), a slewing unit (gears and a motor), and an operator cab (not shown) in which the operator sits. Tower cranes are designed to be assembled at differing heights for construction of buildings of differing heights and disassembled for transportation. The height of the tower crane is adjusted by adding a chosen number of mast sections onto the mast. The height of the tower crane also directly increases the forces to which the pins or connecting elements of the mast sections are subjected.
European Patent Specification No. 0720961 gives example figures of the types of weights that connecting members for mast sections of a tower crane are designed to withstand. Tremendous shear stresses on the connecting component can be caused by, for example, the “over 2268 kg” weight, that may be one of the elements being fastened. It should be noted that additional tower crane components may be further stacked on top the mast sections being fastened.
In view of the large magnitude of the above-mentioned example shear stress for mast sections of a tower crane, it can be appreciated that pins used to join two or more construction machinery components, such as those found in tower cranes, overhead cranes, bridge cranes, aircraft and other engineering equipment, can be exceedingly difficult to remove from the components which they couple.
Difficulty of insertion and removal of a pin from an aperture, however, may additionally or alternatively be dependent on the tolerance of the aperture within which the pin is fitted. A tight fit may be required for design purposes. In such case even a pin used to couple two or more components of a relatively small object, not subjected to large loads, such as an office stapler, may be difficult to insert or remove from an aperture to which it is tightly fitted. Alternatively, an aperture which would not have been a tight fit for a pin of a designated cross-section may become so, due to deformation due to loads thereon, corrosion, repeated removal and insertion of pins, etc., thereby causing the aperture to have an expanded or asymmetric shape. Such deformation of the shape of an aperture is known to be corrected by rewelding the aperture, at least for industrial components of the type adapted to withstand high shear forces.